DC to DC voltage regulators are used for maintaining a consistent output voltage for application to digital and analog circuitries within various circuit devices. An applied input voltage may vary for various reasons. However, despite these variances in the input voltage it is necessary to maintain the voltage applied to various internal circuitries at a consistent level that does not adversely effect the operation of the associated circuit. A DC to DC voltage converter adequately provides this functionality. The DC to DC voltage converter includes an inductor therein having a current passing there through. Effectively sensing the zero crossing of this inductor current within the DC to DC converter is an important feature for synchronous DC to DC converters.
The zero crossing detection of the inductor current is a critical factor that the DC to DC converter needs in order to determine on/off state of the low side switching transistor in order to save energy and improve the overall efficiency at the DC to DC converter. Improving the efficiency will enable the extension of the battery life of the associated electrical circuit. In prior art environments, the inductor current zero crossing is detected by sensing voltage through the low side switching transistor. Typically, when determining zero inductor current, a determination is made when the current decreases from a particular value to zero. The inductor current decreases only when the low side switching transistor is turned on. This makes traditional zero crossing sensing techniques applicable only during the on condition of the low side switching transistor.
However, the use of the low side switching transistor to determine a conductor current zero crossing has certain limitations. One limitation arises when the switching frequency of the switching transistors of the DC to DC converter increases. As the switching frequency increases, the switching cycle becomes shorter. Therefore for the same duty cycle, both the turn on and the turn off time become smaller. At particular points, the turn on time of the low side switching transistor is so short that the length of time that the transistor is turned on is not sufficient to enable a sensing device to respond to the “on” state of the low side switching transistor. This causes a problem with using the low side switching transistor “on” condition as an indication of zero crossing inductor current sensing. Thus, there is a need for a an improved method for detecting inductor current zero crossings in a DC to DC converter.